2. Field of the Invention
The invention relates to a method and apparatus for cleaning workpieces such as sand-casted automobile engine blocks, and more particularly, to such a method and apparatus wherein workpieces are advanced past a cleaning station by means of an oscillating mechanism.
3. Description of the Prior Art
After automobile engine heads, manifolds, blocks, or like articles have been sand-casted, it is necessary to remove remaining traces of sand, scale, and other debris in order to perform further work operations on the parts. A particularly effective apparatus for cleaning such parts (hereafter referred to for convenience as "workpieces") is set forth in the Axi-Flow Patent. In the Axi-Flow Patent, workpieces are advanced successively through an elongate barrel having a skeletal wall construction open at both ends. The barrel is long enough to permit the longitudinal passage of a single line of workpieces through the barrel. As workpieces are advanced through the barrel, the barrel is rotated. A plurality of abrasive throwing wheels are positioned adjacent the barrel to project abrasive particles at high speed through the skeletal walls onto workpieces being advanced through the barrel. By appropriate control of the speed of travel of the workpieces through the barrel, and by rotating the barrel at appropriate speeds (or not rotating it at certain times), almost all surfaces of the workpieces can be cleaned quite effectively. Production rates are very flexible, with an upper limit on the order of 800-1200 workpieces per hour.
Although the Axi-Flow Patent provides an exceedingly effective workpiece cleaning apparatus, certain problems remain. One of these problems relates to cleaning the ends of the workpieces. In the Axi-Flow Patent, a conveyer is provided to deliver workpieces sequentially to the feed end of the barrel. A pusher is provided to push individual workpieces into the barrel and against preceding workpieces such that the line of workpieces in the barrel is in end-to-end contact. Although the Axi-Flow Patent sets forth several techniques by which the ends of workpieces could be cleaned better, such as by casting spacers in place at the ends of the castings or by orienting alternate workpieces at right angles to adjacent workpieces, no totally effective automatic technique is available to clean the ends of the workpieces. The Axi-Flow Feeder Patent, although providing an effective technique for presenting workpieces to the feed end of the barrel, still does not address the problem of cleaning the ends of the workpieces.
An additional concern not addressed by the Axi-Flow Patent and the Axi-Flow Feeder Patent is that of the size and configuration of the workpieces that can be advanced through the barrel. That is, it is necessary for the barrel to be carefully sized relative to the workpieces in order to prevent jamming of the workpieces as they are pushed through the barrel. If it is attempted to provide a larger barrel in order to handle differently sized workpieces, jamming can occur. Jamming is thought to occur through skewing of one or more workpieces relative to the longitudinal axis of the barrel or through two workpieces being wedged tightly together so as to block the barrel. Although the Axi-Flow Patent and the Axi-Flow Feeder Patent set forth machines which operate effectively to clean workpieces at a high rate of speed, these machines lack a certain degree of versatility. The capability to accommodate differently sized workpieces can be obtained only by providing a variety of barrels that relatively closely conform to the configuration of the workpieces, or by providing barrels that have adjustable components.
The Trans-Bar Machine Patent and the Uni-Bar Machine Patent represent two attempts to solve the previously referenced problem of spacing the workpieces in the barrel such that the ends of the workpieces can be cleaned properly. Both the Trans-Bar Machine Patent and the Uni-Bar Machine Patent employ mechanisms which extend into the barrel to engage the workpieces and advance the workpieces through the barrel. The engaging and advancing mechanisms are operated such that a certain spacing of the workpieces occurs. As the workpieces are advanced through the barrel, the mechanisms successively are moved relative to the workpieces in order to engage succeeding workpieces and advance the succeeding workpieces through the barrel.
Because the Trans-Bar Machine Patent and the Uni-Bar Machine Patent cause the workpieces to be spaced during their passage through the barrel, automatically cleaning the ends of the workpieces no longer is a problem. Unfortunately, the production capability of these machines is less than that of the Axi-Flow Patent due to the time required to perform all of the mechanism motions. Accordingly, the Trans-Bar Machine Patent and the Uni-Bar Machine Patent are limited to approximately 600-800 parts per hour versus approximately 800-1200 parts per hour for the Axi-Flow Patent. Moreover, the very existence of mechanisms which extend into the barrel and are impinged by abrasive particles creates a maintenance problem. Additionally, the Trans-Bar Machine patent and the Uni-Bar Machine Patent do not address the problem associated with jamming workpieces in the barrel where the workpieces are not closely sized relative to the barrel.
One device is known wherein workpieces are passed through a cleaning apparatus without the need for pushing the workpieces end-to-end or without providing workpiece engaging and advancing mechanisms. The device in question employs a vibratory conveyor having longitudinally extending frame members which closely conform to the cross-sectional dimensions of the workpieces. In order to orient the workpieces at different attitudes relative to abrasive particle throwing wheels, different sections of the frame members are oriented at different fixed positions relative to the throwing wheels. The type of vibratory drive provided for the conveyor subjects the workpieces to a jolting action in an attempt to cause sand to be loosened and drained from intricate passages or cores in the workpieces.
Unfortunately, the device in question is not as effective as desired. The use of frame members fixed in position relative to the throwing wheels does not provide the same flexibility as does a rotating barrel construction. In effect, it is more difficult to direct abrasive material onto all surfaces of the workpieces. Moreover, because the frame members closely conform to the cross-sectional configuration of the workpieces, the possibility of jamming still exists. The device lacks the capability to accept workpieces of different sizes. Additionally, the jolting action to which the workpieces are subjected is not thought to be effective in loosening and draining sand and scale from internal passages.
Other devices are known wherein workpieces are passed through a cleaning apparatus without the need for pushing the workpieces end-to-end or without providing workpiece engaging and advancing mechanisms. The referenced devices operate much like barrel tumblers and employ a trough-like barrel having a top opening and openings at each end. The barrel is inclined relative to the horizontal so that the feed end is higher than the exit end. The barrel is oscillated about a longitudinal axis while workpieces are deposited into the feed end and abrasive particles are blasted through the top opening. This arrangement is effective because the abrasive particles are blasted directly onto the workpieces without having some of the particles impinge intervening portions of the barrel.
Despite the advantage of the referenced devices in avoiding blasting portions of the barrel, certain problems remain. Because the bed depth and the horizontal slope of the barrel are important factors in how fast workpieces can be advanced through the barrel, and because these factors are constant for a given machine, the referenced devices cannot readily be adjusted for different desired production rates. Further, the referenced devices cannot accurately control the axial speed of a single line of workpieces, in part because workpieces can tumble axially as they advance through the barrel. Additionally, the bed depth of the barrel is such that workpieces can be buried under other workpieces and thereby shielded from the blast. In those cases where it is desired to change the type of workpieces being cleaned in the barrel, it is necessary to shut down the referenced devices in order to remove workpieces remaining at the bottom of the barrel; this is caused by the failure of the referenced devices to provide a positive drive for advancing workpieces through the barrel.